Comment by shikhar

(Founder) We are happy for S2 API to have alternate implementations, we are considering an in-memory emulator to open source ourselves. It is not a very complicated API. If you would prefer to stick with the Kafka API but benefit from features like S2's storage classes or having a very large number of topics/partitions or high throughput per partition, we are planning an open source Kafka compatibility layer that can be self-hosted, with features like client-side encryption so you can have even more peace of mind.